Okay I'm gonna to put this in real life perspective. Slander is technically a crime so if this not true, the radio station committed slander. Now we must also not fail to remember that slander is considered the Defamation Law and is federal and closely related to the first amendment.
HOWEVER, The First Amendment states that "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances." - Bill Of Rights and must commonly known as "Freedom of speech and press".
Answer: IF the radio ad is true, the station or creator is proctected by the first amendment, if not the defamation law may apply and the one it was directed to may sue the station or creator.
